Because insulin and glucagon stimulate canalicular bile secretion we recently observed that intravenous infusion of glucagon in submaximal doses significantly inhibited biliary cholesterol excretion in dogs. The secretion of intravenously administered sodium taurocholate was unaffected by glucagon. We propose to investigate whether glucagon in "physiologic doses" influences biliary lipid excretion and whether endogenously secreted glucagon alters biliary lipid excretion. Also dogs will be treated with triparanol to block reduction of desmosterol to cholesterol. By observing the distribution of desmosterol between bile and plasma during control studies and glucagon infusion, an estimation of the influence of glucagon on the biliary secretion of newly synthesized neutral sterol will be possible. By performing such studies using the injection of 14 C mevalonate, an estimate of the contribution of newly synthesized neutral sterol and equilibrated cholesterol to bile acid synthesis can be estimated and the influence of glucagon on that process will be observed. Studies are described to observe the influence of glucagon on the movement of free cholesterol from plasma lipoprotein into bile. Lastly, a computer model will be employed to study the effect of glucagon on biliary cholesterol excretion.